Vacuum furnaces for heat treating, brazing, sintering, and other heat processing generally run cycles with heating ramps that are controlled or uncontrolled to some set point temperature. The parts, load, or work are then cooled down. Cooling modes include vacuum or non-circulated inert gas cooling, forced gas cooling via circulation, controlled cooling, or a combination of different cooling steps.
There are two types of forced circulated inert gas cooling designs commonly used. The first type involves mounting the blower, fan, and motor assembly with heat exchanger internally to the main vacuum vessel. Alternatively, these parts can also be mounted outside of the vacuum chamber via piping connections. Both approaches work; however, the internal type of cooling arrangement tends to require higher and more frequent maintenance due to the proximity of the moving parts to the heated areas.
Further, many loads being cooled in such furnaces are not uniform in density or mass. Instead, they often have bases with greater densities or hearth masses. As a result, the uniform cooling provided by traditional furnaces causes certain portions of the load to cool at a higher rate resulting in warping or other damage to the load.
This invention relates to controlled and directional cooling to provide optimum metallurgical results while minimizing distortion on the parts being processed within the vacuum furnace. This concept has been used for furnaces with internal cooling arrangements, and directional cooling for such an arrangement has been traditionally achieved via moving baffles. These baffles are, however, directly exposed to the heat inside the furnace. As such, they tend to warp and thus fail to open or close to the desired set point resulting in poor performance. The present invention uses an external arrangement that removes the dangers involved in using internal parts and thus provides reliable, repeatable, and predictable performance and results.
Currently, external gas cooling arrangements use a design that cools the entire internal chamber uniformly or that divides the internal chamber, or plenum, into three or four circumferential rings. The multiple circumferential plenum design provides the capability for different levels of cooling from the front to the rear of the chamber; however, such a design still results in a great deal of distortion. Most loads have a different hearth mass at the bottom as opposed to somewhere along the length, so lengthwise difference in cooling rate still results in uneven cooling and the possibility of warping or damage to the load. Other furnaces have been produced where gas circulates through an internal chamber in the plenum and enters the hot zone enclosure of the plenum through nozzles; however, such an arrangement still provides uniform cooling. Even in designs where the plenum does not completely wrap around the entire hot zone enclosure, the plenum wraps around a significant portion of the hot zone enclosure (e.g., 95%), and the nozzles are positioned in such a manner as to still provide uniform cooling. The present invention is directed at an external gas cooling arrangement providing directional cooling from non-circumferential sectors so that different levels of cooling may be applied to the load from different sections of the circumference of the plenum.